Sunbeam Posted August 1, 2023 Share Posted August 1, 2023 Hi all. I am an electrical numpty so please bear with me. I purchased an internally regulated alternator for my Fiat 125 in order to do away with the (faulty) external reg. The alternator I bought is meant for a late 70’s Spider. Here is the wiring diagram for the charge relay which gets deleted. It is item 16 with the alternator being 10 and the external reg 20. My 125 special parts car is wired thus. My 125 road car is not, with power to terminal 87 NOT provided by a yellow/black jumper from 86, but a separate blue/white from the loom which has its own switched 12V. Does the same job I guess. Now, the Fiat internet is full of instructions on how to arrange the wires and they all assert that you simply remove the yellow and blue from the relay and join them together while deleting the grey wire altogether. This does NOT work and even I can figure out it’s because the yellow excite wire isn’t getting power from anywhere and by extension the bulb in the dash (blue wire) isn’t getting power either! Leaving the relay wired up, I get a nice stable 14 volts to the battery, but the charge light works in the opposite sense. If I add a switched ignition feed to the blue/yellow combo I do get a charge light, and a steady 14v, BUT the light doesn’t go out, and the car doesn’t switch off (because the yellow wire is now feeding alternator volts backwards to the fuse block I guess) Is anybody out there able to offer advice? I’m sure it’s simple to anyone who understands electrons… Quote Link to comment Share on other sites More sharing options...
Unclejake Posted August 2, 2023 Share Posted August 2, 2023 5 hours ago, Sunbeam said: If I add a switched ignition feed to the blue/yellow combo I do get a charge light, and a steady 14v, BUT the light doesn’t go out, and the car doesn’t switch off (because the yellow wire is now feeding alternator volts backwards to the fuse block I guess) You probably need to add a diode into that circuit. Diodes are available from the likes of Jaycar and will cost less than $2, but you'll need to solder it in. Think of a diode as a one way valve for electricity. Solder in a diode into the wiring you've described above. You should be able to work out where, and in what direction you want the diode to operate - but from your description it probably needs to go into that yellow wire. 2 1 Quote Link to comment Share on other sites More sharing options...
Sunbeam Posted August 3, 2023 Author Share Posted August 3, 2023 Cheers for the hint. Makes sense I guess. Could go in the yellow or the +12v feeder. Quote Link to comment Share on other sites More sharing options...
dmulally Posted August 7, 2023 Share Posted August 7, 2023 From my fading memory the band on the diode should be on the alternator end. It's why I use a boring old one wire alternator these days and an altmeter. Bulletproof and simple. Quote Link to comment Share on other sites More sharing options...
azzurro Posted August 7, 2023 Share Posted August 7, 2023 Ill have a look at mine, i have an internally regulated alternator on my 125 - from memory it was as simple as unplug the voltage regulator and plug a couple of those wires together, but exactly which i cant recall. Im probably explaining it wrong, but in my mind, the alternator light on the dash works on the basis of who is winning the Battle of the Volts (path of least resistance?) between the alternator and the battery, if the alternator is pushing out more pressure (volts) than the battery, the pixies can then take the path that avoids the lamp (which is also a resistor - that why you cant use a LED there), but if the battery is winning, the path though the bulb is taken instead (cant push though the regulator??) and so it lights up. How that relates to the wiring idk, but now my brain is mush, and you are now stupider for reading this, ill go take a look and report soon 1 Quote Link to comment Share on other sites More sharing options...
Lord Gruntfuttock Posted August 7, 2023 Share Posted August 7, 2023 I swapped from external reg to internally regulated new alternator in a '71 Ford. From memory I jumped between 2 connectors on old reg and it all worked. Except it drains if left. Suspect I need to install a diode somewhere too... Quote Link to comment Share on other sites More sharing options...
morkster Posted August 7, 2023 Share Posted August 7, 2023 This may or may not help you but look at the diagrams on the first page here: https://www.ausrotary.com/viewtopic.php?t=33676 I used one of them when i did my rx2.. Bottom line is B+ post to battery+, Sensor to battery+, and Light to charge indicator and ignition (through relay). And two 6amp diodes on light circuit to stop power flow out. Quote Link to comment Share on other sites More sharing options...
Sunbeam Posted September 25, 2023 Author Share Posted September 25, 2023 On 08/08/2023 at 08:53, azzurro said: Ill have a look at mine, i have an internally regulated alternator on my 125 - from memory it was as simple as unplug the voltage regulator and plug a couple of those wires together, but exactly which i cant recall. ill go take a look and report soon I am awaiting your report sir. Quote Link to comment Share on other sites More sharing options...
azzurro Posted September 25, 2023 Share Posted September 25, 2023 I have already clearly explained precisely what to do, in my earlier post, which I refer you to below, for your convenience On 08/08/2023 at 08:53, azzurro said: ...as simple as unplug the voltage regulator and plug a couple of those wires together, but exactly which i cant recall... ....Im probably explaining it wrong, but .... ....who is winning the Battle of the Volts... (path of least resistance?) ...the pixies can then take the path that avoids the lamp ..How that relates to the wiring idk... I said good day, Sir 4 Quote Link to comment Share on other sites More sharing options...
sr2 Posted September 25, 2023 Share Posted September 25, 2023 Is it a 2, 3 or 5 wire alternator? Quote Link to comment Share on other sites More sharing options...
Sunbeam Posted September 25, 2023 Author Share Posted September 25, 2023 9 hours ago, sr2 said: Is it a 2, 3 or 5 wire alternator? New one is a 2 wire Quote Link to comment Share on other sites More sharing options...
azzurro Posted September 26, 2023 Share Posted September 26, 2023 I had a look at my 125's set up and consulted the wiring diagrams to confirm what ive done the thin signal wires from the alternator to regulator (giallo) and regulator to IGN light (azzurro) wires are joined together - direct line from the later model (Lancia Delta ie i think? ) internally regulated alternators signal output direct to the dash light. the thicker main supply wires from the alternator output post to regulator (grigo) and then regulator to fuse box (rosa) are* also connected together. *i have strung a new main cable to a relay to take the load off the ignition and light switches, but yeah, basically its straight bypass of the old regulator Quote Link to comment Share on other sites More sharing options...
Sunbeam Posted September 26, 2023 Author Share Posted September 26, 2023 Hmmm. I don’t have a ROSA wire, and the yellow/blue connection trick doesn’t work for me. I think I must have a different alternator because the yellow wire must have a power supply or the alternator puts out 0 volts Quote Link to comment Share on other sites More sharing options...
Unclejake Posted September 26, 2023 Share Posted September 26, 2023 Did you try the $2 diode as suggested early August? From your description it will solve your issues. The charge light on the dash is usually an essential part of the circuit to excite the alternator. Fiats are odd, but not that odd.... and also be certain you're understanding your charge light (and if it's switched from earth or positive) correctly Quote Link to comment Share on other sites More sharing options...
Sunbeam Posted September 26, 2023 Author Share Posted September 26, 2023 I have one (diode) but haven’t reinstalled the new alternator yet as I’ve been running it on the old one for now. Quote Link to comment Share on other sites More sharing options...
azzurro Posted September 27, 2023 Share Posted September 27, 2023 17 hours ago, Sunbeam said: Hmmm. I don’t have a ROSA wire, and the yellow/blue connection trick doesn’t work for me. I think I must have a different alternator because the yellow wire must have a power supply or the alternator puts out 0 volts yours is a later model than mine i think so colours may vary but basically your hooking the two pairs that go to/from the external regulator together (the two fat wires whcih are the main feed to the car fuse box, and the two skinny ones which deal with the lamp). there may also be a lamp relay under the hood which might complicate matters. pretty sure you need to bench test the alternator with a load and a light/12v as per the setup you would have on the car or it wont output anything (the lamp is an 'exciter'). Mine is a 'single wire' which means there is only one control wire (and one main feed which isnt counted) - i think you said yours is a two wire (which i take to mean two control wires + main feed) If its a two wire you are outside of my experience, but maybe a pic of the back of it or the labels for the pins could help figure out what what they do and how to hook it up? Quote Link to comment Share on other sites More sharing options...
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